This invention relates to a method for reducing emissions due to gaseous decomposition products of an electrolyte of electrochemical storage devices in a motor vehicle.
Recently, electrochemical storage devices, preferably energy storage devices composed of double-layer capacitors for storing and supplying electric energy, are being used more frequently in motor vehicles. However, some of the liquid electrolytes decompose over the lifetime of these storage devices, forming gaseous decomposition products. This occurs in particular with additional exposure to elevated temperatures, such as those occurring in motor vehicles. The decomposition products are usually collected in the storage device and discharged to the outside through a vent hose. Such a device is disclosed in DE 101 28 672 A1.
However, depending on the type of electrolyte, the resulting gaseous decomposition products may contain a number of elements and compounds that are toxic and/or explosive and/or whose emission is prohibited by law.
To prevent the gaseous decomposition products from entering the environment as emissions, DE 101 28 672 A1, which was cited above, discloses agents that are capable of binding the gaseous decomposition products thereby emitted. These agents may be, for example, absorber materials. However, no further details are discussed.
The object of the present invention is thus to provide an alternative or improved method for reducing emissions due to gaseous decomposition products of an electrolyte of electrochemical storage devices.
The inventive method for reducing emissions due to gaseous decomposition products of an electrolyte of electrochemical storage devices in a motor vehicle, preferably double-layer capacitors having organic solvents as the electrolyte, is characterized in that the gaseous decomposition products are sent to an activated carbon filter and/or a molecular sieve for deposition of at least a portion of the decomposition products.
An activated carbon filter has a carbon structure with a large internal surface area capable of storing a plurality of compounds and elements such as hydrocarbons, nitrites or organic carbonates. The gaseous decomposition products of an electrolyte include, for example, hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO) and ethylene (C2H2). If the decomposition products are sent to the activated carbon filter, they are deposited on the porous surface of the activated carbon and therefore do not reach the environment.
In contrast with the activated carbon filter in which the decomposition products are deposited on the surface, molecular sieves are natural or synthetic zeolites having a high absorption capacity for gases, vapors and dissolved substances. Suitable molecular sieves include types 3A, 4A and 5A, for example.
Since the molecular sieve is an absorber material, it may happen that over a period of time this absorber material becomes saturated, i.e., it can no longer absorb any gaseous decomposition products. For this reason, the absorber material should be designed with large enough dimensions to be able to take up the total quantity of decomposition products expected to occur during the lifetime of the vehicle. As an alternative to that, the absorber material may also be replaced as a service measure at certain intervals.
In the embodiment using an activated carbon filter, since the gaseous decomposition products are deposited only at the surface of the activated carbon in an activate carbon filter, the activated carbon filter may advantageously be flushed at predetermined points in time or at predetermined operating points, so that the decomposition products that had been deposited in the activated carbon filter can be sent to the internal combustion engine. In this way, the activated carbon filter is cleaned again of the decomposition products that have already been deposited and it can thus absorb new decomposition products again. The decomposition products sent to the internal combustion engine are incinerated.
A special advantage when using an activated carbon filter as an absorber material is that most new vehicles are currently already equipped with an activated carbon filter for absorbing the gaseous fuel, which is gaseous due to the high temperature. To be able to absorb at least a portion of the decomposition products of the electrolytes of electrochemical storage devices in the motor vehicle, an airtight connecting unit between the electrochemical storage devices and the activated carbon filter for supplying the decomposition products is provided in the motor vehicle. The airtight connecting unit may be, for example, a tube which connects the storage devices either directly to the activated carbon filter or to the airtight connecting unit between the fuel tank and the activated carbon filter. Likewise, when using a molecular sieve as the absorber material, the device includes an airtight connecting unit between the electrochemical storage devices and the molecular sieve.
As an alternative to the inventive method using the aforementioned absorber materials, the second inventive method for reducing emissions due to gaseous decomposition products of an electrolyte of electrochemical storage devices in a motor vehicle, preferably double-layer capacitors having organic solvents as the electrolyte, is characterized in that the decomposition products are sent to a chemically reactive material and/or a catalytically active material for conversion of at least a portion of the decomposition products.
In contrast with the aforementioned absorber materials, in this method the decomposition products are not absorbed but instead are converted or split, forming compounds that are of little or no harm to the environment. The amount of the chemically reactive material used must be large enough to be able to absorb the expected total amount of decomposition products that will occur during the lifetime of the vehicle. As an alternative to this, the chemically reactive material may also be replaced as a service measure.
Copper oxide is advantageously used as the chemically reactive material.
In contrast with a chemically reactive material such as copper oxide, which enters into the conversion of the decomposition products, the catalytically active material does not enter into the reaction but instead accelerates the reaction by reducing the activation energy. Elements and compounds such as hydrogen that react especially easily may thus be converted even at room temperature. Since the mass flow of decomposition products to be expected is comparatively low, the catalyst may be kept small. Another advantage when using a catalyst is that the temperature increase in the vehicle remains low.
The various inventive methods may advantageously be combined, so that all the decomposition products that occur are absorbed and/or converted almost completely.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings for example.